Refrigerant system with pulse width modulation for reheat circuit

ABSTRACT

A refrigerant system incorporating a reheat circuit is also provided with pulse width modulation control to adjust the amount of refrigerant being compressed. In particular, in any dehumidification mode of operation, by activating the pulse width modulation control, sensible and latent components of capacity can be controlled independently and with significantly better accuracy. The present invention provides the ability to precisely tailor both humidity and temperature control to the conditioned space demands utilizing less expensive components and in a more efficient manner than in the prior art.

BACKGROUND OF THE INVENTION

This application relates to a pulse width modulation control for arefrigerant system with a reheat circuit.

Refrigerant systems are known and utilized to provide and maintaindesired temperature and humidity levels of air being delivered into aconditioned environment. Examples would include air conditioners andheat pumps of various configurations and design schematics. As known,the refrigerant system acts to change the temperature of the air beingdelivered into the environment to match a desired temperature. Further,the refrigerant system controls the humidity level in the environment,typically within the comfort zone.

Various operational features and enhancement options are known forproviding adjustments in refrigerant system capacity. One approach,which has been utilized in the prior art to change the capacity of aconventional refrigerant system, is the use of a pulse width modulationtechnique to control a valve on a compressor suction line from a fullyopen to a fully closed position. By cycling this valve at a certainrate, utilizing a pulse width modulation approach, an additional degreeof capacity control is provided for a refrigerant system in a veryefficient manner. Since the pulse width modulation technique maintainscompressor operation between fully loaded and fully unloaded states,ideally, no additional losses are incurred during such part-loadoperation of a refrigerant system, in comparison to other knownunloading methods such as suction throttling, hot gas bypass, etc.

One other variation of the pulse width modulation approach mentionedabove is an employment of a scroll compressor, wherein a pulse widthmodulation technique is utilized to allow the scroll compressor membersto be moved into and out of contact with each other at a certainperiodic rate. As above, when the scroll members are out of engagement,little or no compression occurs. On the other hand, when the scrollmembers are in contact with each other, full-load operation is resumed.Once again, since the compressor is operated between loaded and unloadedstates, only a minimal additional loss is incurred.

One other type of control provided in a refrigerant system isdehumidification control delivered by a reheat circuit. A reheat circuittypically taps refrigerant at a temperature somewhat higher than thetemperature of refrigerant in an evaporator. When a reheat circuit isactivated, the evaporator cools air being delivered into a conditionedenvironment to a temperature below the desired temperature. This allowsfor a greater moisture removal potential from the supply airstream,while the air passes over the evaporator. Downstream the overcooled anddehumidified air flows over a reheat heat exchanger, where itstemperature is raised back to a desired level, but now at a lowerhumidity.

As known, there are a number of variations of dehumidification systemschematics for providing such reheat control. For instance, one widelyused concept employs hot refrigerant vapor exiting compressor dischargeport. An alternative popular approach involves a subcooled liquid, or atwo-phase refrigerant mixture utilized for reheat purposes. Although allof these various schemes typically provide only a step function (on oroff) to switch between conventional cooling and the utilization of areheat circuit, attempts have been made in the past to split and/orregulate refrigerant flow between the main circuit and the reheat branchto provide finer control than “full off” or “full on” operation. Theseattempts have faced some challenges in terms of system reliability,stability and robustness.

Recently, an invention of the assignee of the present invention proposedto utilize variable speed drives for various components such ascompressors or fans to allow for refrigerant and airflow variations toadjust performance of a reheat circuit. However, these attempts wouldnot always provide fully satisfactory results and cover a somewhatnarrow range of applications. Further, regulatory requirements,concerning minimum fresh air circulation rates in a conditioned space,made this task even more difficult to accomplish. Also, there areefficiency losses and reliability concerns associated with variablespeed drives.

On the other hand, the pulse width modulation techniques mentioned aboveallow for a wide range of control to the provided capacity, and in manycases can be executed less expensively and more efficiently than the useof a variable speed drive approach.

Further, in a co-pending PCT application owned by the assignee of thepresent invention and entitled “SYSTEM REHEAT CONTROL BY PULSE WIDTHMODULATION” and identified by PCT Serial No. US05/30603, a technique isdisclosed for utilizing pulse width modulation to control the openingand closing of the valve that taps refrigerant into the reheat circuit.While the disclosed method provides greater refrigerant system capacitycontrol, other advanced methods of achieving similar control have beendevised.

SUMMARY OF THE INVENTION

In the disclosed embodiment of this invention, a pulse width modulationcontrol is incorporated into a refrigerant system having a reheatcircuit. In one embodiment, the pulse width modulation control device ispositioned on a suction line delivering the refrigerant to thecompressor. By controlling the amount of refrigerant being directed tothe compressor, while the reheat mode is activated, an advanced finerdehumidification control is provided than as in the past. The pulsewidth modulation becomes a very effective instrument for controllingrefrigerant flow, which allows for independent and accurate control ofsensible and latent components of capacity in response to a constantlychanging thermal load in a conditioned space. The technique is similarto utilizing a variable speed compressor to control the sensible andlatent capacity, but achieves this control at a much lower cost, reducedcomplexity and higher efficiency. The pulse width modulation conceptprovides a straightforward method to achieve the desireddehumidification results by varying a sensible heat ratio in combinationwith the activation of a reheat function. This allows for enhancedhumidity control and flexibility in system operation over a wide rangeof environmental conditions, while any mechanicaldehumidification/reheat concept can be utilized. As a result, theproposed approach reduces variation in temperature and humidity in aconditioned space and subsequently improves the comfort of an occupant.

In a disclosed embodiment, a valve for bypassing at least a portion ofrefrigerant around a condenser may also be controlled utilizing a pulsewidth modulation technique. Typically, this condenser bypass providesrefrigerant at a higher temperature to the condenser exit and is engagedwhen dehumidification with less sensible cooling is required in aconditioned environment. When at least a portion of refrigerant isbypassing the condenser, more heat is rejected by a reheat coil into theairstream delivered to a conditioned space and thus less overallsensible cooling will be provided to the air.

In another embodiment, the pulse width modulation to control the amountof refrigerant being delivered through the refrigerant system having areheat circuit occurs in a scroll compressor, and allows the compressorscroll members to engage and disengage to control the amount ofrefrigerant being delivered through the refrigerant system. When thescroll members are out of engagement, little or no compression occurs.On the other hand, when the scroll members are in contact with eachother, full-load operation is resumed.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one example schematic of a refrigerant system.

FIG. 2 shows an alternative method of providing pulse width modulationcontrol to a compressor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A refrigerant system 20 is illustrated in FIG. 1 incorporating acompressor 22 compressing a refrigerant and delivering it downstream toa condenser 24. An expansion device 26 is positioned downstream of thecondenser 24, and an evaporator 28 is positioned downstream of theexpansion device 26. Refrigerant circulates between these four basiccomponents, as known. A fan 25 moves air over the condenser 24.

The refrigerant system 20 is also provided with a reheat circuit. Thereheat circuit incorporates a three-way valve 30 for selectivelydelivering refrigerant into and through a reheat heat exchanger 32. Acheck valve 34 ensures that refrigerant only flows from the valve 30through the heat exchanger 32 and through the check valve 34unidirectionally, and re-enters the main refrigerant circuit at ajunction point 33. As illustrated, the refrigerant is tapped through thereheat heat exchanger 32 downstream of the condenser 24, and is returnedupstream of the expansion device 26. This is only one example and isillustrative of the reheat circuit schematics, and many otherconfigurations are feasible. Reheat circuit methods are known which taprefrigerant from any location upstream or downstream of the condensercoil 24 and return the refrigerant to any location upstream of theexpansion device 26 within the refrigerant system 20. The presentinvention would extend to any of those methods. As an example, analternative inlet 200 into the reheat circuit with the heat exchangerupstream the condenser is shown in phantom in FIG. 1.

Another feature illustrated in the FIG. 1 embodiment is a condenserbypass line 36 having a bypass valve 38. Bypass line 36 bypasses atleast a portion of refrigerant around the condenser 24 when the bypassvalve 38 is opened. This would occur when dehumidification is to beperformed with the reduced sensible cooling demand in a conditionedspace. When at least a portion of refrigerant is bypassing the condenser24, more heat is rejected by a reheat coil into the airstream deliveredto a conditioned space, and thus less overall sensible cooling willoccur to the air as it would be if it had passed through the condenser24. A shutoff valve 35 is provided upstream of the condenser 24 in caseit is desired for the entire refrigerant flow to bypass the condenser24.

As is known, a fan 27 moving air over the evaporator 28 also moves airover the reheat heat exchanger 32. A control 42 for the refrigerantsystem 20 will generally operate the reheat circuit to provide reheatfunction when dehumidification is desirable with less or no sensiblecooling. Generally, the control 42 operates the refrigerant system 20such that the refrigerant in the evaporator 28, controlled as known,would lower the temperature of the supply airstream below the desiredtemperature in the environment to be conditioned. In this manner,additional moisture can be removed from the air to satisfy humiditylevel in the conditioned environment. The air then passes serially overthe reheat heat exchanger 32 and is heated back up to the targettemperature, since the refrigerant in the reheat heat exchanger 32 issomewhat hotter than the refrigerant in the evaporator 28. The airhaving been reheated by the reheat heat exchanger 32 already has lowerhumidity such that the air will now have the desired temperature anddesired humidity levels.

The condenser bypass line 36 and bypass valve 38 may be operated, asknown, to further provide precise humidity and temperature control. Thisbypass is typically operated when the sensible cooling load isrelatively low, but dehumidification (latent load) is still desirable.Again, the function of such a bypass and its operation to providevariable sensible heat ratios are known.

The present invention relates to the use of pulse width modulationcontrols for the valve 40 and also the bypass valve 38. The pulse widthmodulation allows each of these valves to be cycled at a predeterminedvariable rate (which generally is different for each valve) andcontrolling the amount of refrigerant passing through. Pulse widthmodulation allows for control of the refrigerant flow from approximately5% to 100% of the refrigerant flow at a fully open valve position. Thus,by cycling these valves at specified variable rates, the amount ofrefrigerant passing through the main circuit of the refrigerant system20 and through its branches, and hence the amount of cooling anddehumidification provided to a conditioned environment, can be preciselycontrolled.

When the refrigerant system 20 operates in a conventional cooling mode(the reheat branch and condenser bypass are typically not active), thepulse width modulation valve 40 offers the means of overall coolingcapacity adjustment by varying the cycling rate and engagement timeinterval. Consequently, when time-averaged refrigerant flow delivered bythe compressor 22 is reduced, the refrigerant saturation suctiontemperature decreases as well. As a result, although overall refrigerantsystem capacity is reduced, the evaporator 28 would provide betterrelative dehumidification capability and operation at a variablesensible heat ratio. On the other hand, an absolute amount of moisturebeing removed from the airstream may be reduced. Therefore, in theconventional mode of operation, although pulse width modulationtechnique presents a significant opportunity to provide part-loadperformance over a wide range of capacities, system dehumidificationcapability control is narrow and restricted.

When the reheat branch of the refrigerant system 20 is engaged, thedehumidification mode is activated, and significant moisture removaloccurs in the evaporator 28. In this mode of operation, overall systemsensible cooling capacity is noticeably reduced, but not completelycounterbalanced by the reheat coil 32. Once again, the pulse widthmodulation valve 40 allows for the fine-tuning of both sensible andlatent capacity components, but now around a different operational pointprovided by a reheat function.

Further, when the condenser bypass is activated, it provides a furthermeans of sensible capacity reduction and system dehumidificationoperation in the vicinity of a neutral sensible capacity point. Asbefore, the pulse width modulation valve 40 offers fine sensible andlatent capacity adjustments. Moreover, if the bypass valve 38 iscontrolled in a pulse width modulated manner as well, a sensible heatratio can be varied over a wide spectrum of values to satisfy thermalload demands and application requirements. Note that without pulse widthmodulation control a true neutral sensible capacity may be achieved onlyat a single set of environmental conditions and, at off-designconditions, the refrigerant system 20 would provide either cooling orheating. Thus, integration of the pulse width modulation valves 40 and38 into the system design allows for achieving neutral sensible capacityat a wide spectrum of operating conditions as well as independentlyadjust system cooling and dehumidification capability.

As a result of pulse width modulation control, variations of temperatureand humidity in a conditioned environment can be greatly reduced,providing more comfort to the space occupant.

FIG. 2, as an example, shows a scroll compressor 154 including anon-orbiting scroll member 150 and an orbiting scroll member 152. Asshown, a control 142 controls a pulse width modulation valve 144, whichcontrols the flow of a pressurized fluid from a line 146 into a backpressure chamber 148. As is known, the back pressure chamber 148 holdsthe non-orbiting scroll member 150 against the orbiting scroll member152. When the pulse width modulation valve 144 blocks the flow of thispressurized fluid, the scroll members are allowed to move away from eachother and little or no compression occurs. On the other hand, when theback pressure chamber 148 is pressurized, the scroll members 150 and 152are fully engaged for full-load operation. Since the compressor isoperated between fully loaded and unloaded states, no significantadditional losses are incurred. Again, this basic technique is known.However, the use of this technique in combination with a refrigerantsystem having a reheat circuit is novel over the prior art. Generally,the FIG. 2 compressor 154 would be substituted for the pulse widthmodulation suction valve 40 and compressor 22 of the FIG. 1 embodiment.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

1. A refrigerant system comprising: a compressor for compressingrefrigerant and delivering it downstream to a condenser, an expansiondevice positioned downstream of said condenser and an evaporatorpositioned downstream of said expansion device; a reheat circuitincorporated into said refrigerant system, said reheat circuit beingoperable to tap at least a portion of refrigerant from a mainrefrigerant circuit and pass the refrigerant through a reheat heatexchanger, the refrigerant having passed through the reheat heatexchanger being returned to the main refrigerant circuit, an air-movingdevice for moving air over said evaporator, and then serially over saidreheat heat exchanger; and a component having pulse width modulationcontrol for controlling the amount of refrigerant being compressed bysaid compressor, and a control for controlling said component to varythe amount of refrigerant passing from said compressor to achieveprecise control over both temperature and humidity provided by therefrigerant system.
 2. The refrigerant system as set forth in claim 1,wherein said component is a suction valve for controlling the amount ofrefrigerant delivered through said suction valve and to said compressor.3. The refrigerant system as set forth in claim 1, wherein saidcomponent is the compressor, and the pulse width modulation controlcontrolling the amount of refrigerant compressed by said compressor. 4.The refrigerant system as set forth in claim 3, wherein said compressoris a scroll compressor.
 5. The refrigerant system as set forth in claim1, wherein said reheat heat exchanger is positioned upstream of saidcondenser.
 6. The refrigerant system as set forth in claim 1, whereinsaid reheat heat exchanger is positioned downstream of said condenser.7. The refrigerant system as set forth in claim 1, wherein a bypass lineand associated valve allow to bypass at least a portion of refrigerantaround said condenser when less cooling is needed but dehumidificationis still desirable.
 8. The refrigerant system as set forth in claim 7,wherein said bypass valve is also provided with pulse width modulationcontrol.
 9. The refrigerant system as set forth in claim 7, wherein saidat least a portion of refrigerant comprises entire refrigerant flowdelivered by said compressor.
 10. The refrigerant system as set forth inclaim 1, wherein the pulse width modulation is controlled to provideneutral sensible capacity.
 11. The refrigerant system as set forth inclaim 1, wherein the pulse width modulation is controlled to providevariable sensible heat ratio.
 12. The refrigerant system as set forth inclaim 1, wherein the pulse width modulation is controlled toindependently provide cooling and dehumidification.
 13. The refrigerantsystem as set forth in claim 1, wherein the pulse width modulation iscontrolled to independently provide heating and dehumidification. 14.The refrigerant system as set forth in claim 1, wherein the pulse widthmodulation is controlled to reduce variations of temperature andhumidity in the conditioned environment.
 15. A method of controlling arefrigerant system including the steps of: providing a compressor forcompressing refrigerant and delivering it downstream to a condenser, anexpansion device positioned downstream of said condenser and anevaporator positioned downstream of said expansion device; providing areheat circuit incorporated into said refrigerant system, said reheatcircuit being operable to tap at least a portion of refrigerant from amain refrigerant circuit and pass the refrigerant through a reheat heatexchanger, the refrigerant having passed through the reheat heatexchanger being returned to the main refrigerant circuit, an air-movingdevice for moving air over said evaporator, and then serially over saidreheat heat exchanger; and controlling a component with pulse widthmodulation control to change the amount of refrigerant being compressedby said compressor to achieve precise control over both temperature andhumidity provided by the refrigerant system.
 16. The method as set forthin claim 15, wherein said component is a suction valve for controllingthe amount of refrigerant delivered through said suction valve and tosaid compressor.
 17. The method as set forth in claim 15, wherein saidcomponent is the compressor, and the pulse width modulation controlcontrolling the amount of refrigerant compressed by said compressor. 18.The method as set forth in claim 17, wherein said compressor is a scrollcompressor.
 19. The method as set forth in claim 15, wherein said reheatheat exchanger is positioned upstream of said condenser.
 20. The methodas set forth in claim 15, wherein said reheat heat exchanger ispositioned downstream of said condenser. 21.-34. (canceled)